Priming systems in general have been used for bonding hard tissue. U.S. Pat. No. 4,719,149 describes a primer that is an acid and a water-soluble film former. The acid has a pKa less than or equal to that of phenol and the acid and its calcium salt(s) are soluble in the film former. The primer is free of adhesively detrimental quantities of calcium salts that are not soluble in the film former.